This invention relates to the application of high viscosity release agents upon the surfaces of heated members, and more particularly, to the application of high viscosity release agents upon the surfaces of a fuser member in xerographic copying machines. The invention also relates to the method of manufacture of certain preferred applicators and the article formed thereby.
The present invention is particularly useful in the field of xerography where images are electrostatically formed upon a member and developed with resinous powders known as toners, and thereafter fused or fixed onto sheets of paper or other substrates to which the powder images have been transferred. The resin-based powders or toners are generally heat and/or pressure softenable, such as those provided by toners which contain thermoplastic resins and used conventionally in a variety of commercially known methods.
In order to fuse images formed of the resinous powders or toners, it is necessary to heat the powder, to submit the powder to pressure or to use a combination of heat and pressure to fix or fuse the resinous powders or toners to a particular substrate. Temperature ranges and/or pressure will vary depending upon the softening range of the particular resin used in the toner. When heat is used in conjunction with pressure to fuse the images to a substrate, it is generally necessary to heat the toner powder in excess of about 93.degree. C. or higher. Temperatures as high as 163.degree. C. or even higher are not uncommon in commercially known methods and devices.
It has long been recognized that one of the fastest and most positive methods of applying heat for fusing the powder image is direct contact of the resin-based powder with a hot surface, such as a heated roll while pressure is being applied to the substrate to which the powder image is to be fused or fixed. But, in most instances, as the powder image is tackified by the heat and/or pressure, part of the image carried by the support material will stick to the surface of the plate or roll or any other configuration so that as the next sheet is advanced on the heated surface, the tackified image, partially removed from the first sheet, will partly transfer to the next sheet and at the same time part of the tackified image from said next sheet would adhere to the heated surface. This process is commonly referred to in the art as "offset," a term well-known in the art.
The offset of toner onto the heated surface led to the development of improved methods and apparatus for fusing the toner image. These improvements comprised fusing toner images by forwarding the sheet or web of substrate material bearing the image between two rolls at least one of which was heated, the rolls contacting the image being provided with a thin coating of tetrafluoroethylene resin and a silicone oil film to prevent toner offset. The outer surfaces of such rolls have also been fabricated of fluorinated ethylene/propylene or silicone elastomers coated with silicone oil as well as silicone elastomers containing low surface energy fillers such as fluorinated organic polymers, and the like. The tendency of these rolls to pick up the toner generally requires some type of release fluid continuously applied to the surface of the roll to prevent such offset, and commonly known silicone oils are generally well adapted for this purpose. Not only are the polydimethyl-siloxane fluids well known for this purpose but certain functional polyorganosiloxane release agents have also been described for this purpose. It is also well known to utilize fluids of low viscosity, for example, 100-200 centistokes as well as fluids of relatively high viscosity, for example, 12,000 centistokes to 60,000 centistokes and higher.
It is advantageous to use release fluids, liquids or agents of relatively high viscosities to prevent the offset phenomenon in certain applications. For example, in certain high speed duplicators and copiers, there is substantial improvement of fuser performance when high viscosity release agents are applied upon the heated surfaces used to fix the toner powders to a substrate when the substrate is in pressure engagement with the heated surface. However, because of the high viscosity of the fluids, substantial difficulty is encountered in applying the fluids upon the surfaces of the fuser members. It is for this reason that emulsions of water and high viscosity silicone oil have been atomized and sprayed upon the fuser roll as disclosed in French Pat. No. 2,346,749. The water in such emulsions evaporates when it is atomized upon the fuser roll. Furthermore, this prior art teaches that such applicator devices as wicks and pads require the use of low viscosity release fluids for the effective application of a release agent upon a heated surface used to fix toner powder to a substrate.